Field
The disclosed concept pertains generally to ground fault circuit interrupters (GFCIs), and, more particularly, to a system and method for self-testing the detection circuitry of a GFCI.
Background Information
Electrical circuits generally employ one or more circuit interrupters configured to disable power to a load in response to an overcurrent condition, such as an overload condition or a relatively high level short circuit or fault condition. One such circuit interrupter is a ground fault circuit interrupter (GFCI). A GFCI is a device that disables an electric circuit when it detects that current is flowing along an unintended path, such as through water or through a person. GFCIs are often used to reduce the risk of electric shock. GFCIs are available in two types for permanent installation, the circuit breaker type that may be installed in a circuit breaker panel, and the receptacle type that may be installed in a normal electrical box.
A GFCI works by measuring difference between the current leaving the hot side of the power source and the current returning to the neutral side. If the measured currents are not equal (thus making the difference zero), this means that some of the current is flowing along an unintended path, and the GFCI shuts the power off. When the problem is corrected, the GFCI can manually be reset by pushing a reset button provided as part of the GFCI.
GFCIs are covered by Underwriters Laboratory (UL) Standard UL 943. The Standard UL 943 requires that GFCI devices include a built-in test circuit including a test button which allows a user to periodically manually test the device. When the test button is depressed, a simulated ground fault current is produced that causes the GFCI device to open if the device is operating properly. The device must then be manually reset (for receptacle types, this is done by pressing the rest button to return it to service; for circuit breaker types, this is done by switching the manual handle back to ON).
It is recommended that manually testing of GFCIs be conducted at least one time per month. However, in practice, many GFCIs are not regularly manually tested for proper functionally. Thus, more recently, GFCIs have been developed that employ a self-test functionality that automates the testing process by performing a self-test periodically (e.g., without limitation, every 3 hours, every hour, or every minute) to provide an extra level of safety. Such self-test GFCIs of the receptacle type typically include a status indicator, such as one or more LEDs, to visually indicate the current status of the device (i.e., operational or not operational) so that it can be replaced in the case of a failure. For breaker type GFCIs, the breaker will de-energize (trip) circuit if a self-test does not pass.